1. Field of the Invention
The present invention relates to an apparatus and method for detecting an adaptive motion direction of an image (object).
2. Description of the Related Art
In a first prior art adaptive motion direction detecting method, the following steps are carried out:
1) first two-dimensional pixel data of an object from a pickup camera for preset areas at time t1 is fetched and stored in a first frame memory;
2) second two-dimensional pixel data of the object from the pickup camera for the preset areas at time t2 (>t1) is fetched and stored in a second frame memory;
3) differences between the first and second two-dimensional pixel data stored in the first and second frame memories are calculated; and
4) an image of the object at time t3 (>t2) is estimated to detect a motion direction of the contour of the object.
The above-described first prior art adaptive motion direction detecting method is disclosed in JP-A-6-96210 and JP-8-44852.
In the first prior art adaptive motion direction detecting method, however, since the image of the object has a bright contour and a dark contour which are generally different from each other, the calculated differences between the first and second two-dimensional pixel data depend upon the deviation between the bright contour and the dark contour, so that it is difficult to accurately determine the motion direction of the object.
In the above-described first prior art adaptive motion direction detecting method, in order to accurately determine the motion direction of an object independent of a bright contour and a dark contour thereof, two-dimensional pixel data in each of the present areas are normalized by their maximum lightness and their minimum lightness to form bright contour data and the dark contour data. Then, motion directions of the object are determined in accordance with the bright contour data and the dark contour data, respectively. On the other hand, two-dimensional pixel data in each of the preset areas is caused to be binary data “1” when the lightness thereof is larger than a definite lightness, and two-dimensional pixel data in each of the preset areas is caused to be binary data “0” when the lightness thereof is not larger than the definite lightness. However, these techniques deteriorate the efficiency of motion detection. In addition, the presence of the two frame memories does not save the resource of memories.
A second prior art adaptive motion direction detecting method, spatial and time convoluting integrations are performed upon N-successive images for each local area at times t, t+Δt, t+2Δt, . . . , t+NΔt, to obtain an optical flow, thus detecting a speed of an object (see: JP-A-7-192135).
In the above-described second prior art adaptive motion direction detecting method, however, since means for determining all gradients of the object are required, the resource thereof cannot be saved. That is, images statistically include horizontal displacement; even in this case, spatial and time convoluting interactions for all the directions have to be carried out, which decreases the efficiency of the resource thereof.